The above-mentioned check is carried out in extremely short intervals of time, generally in conjunction with riveting the pull-up ring to the metal can top. Problems arise with presently known and used equipment because such equipment is not fully reliable. As a result, defective metal can tops are produced. The equipment used at present has mechanical linkages with actuator switches to stop production when a fault is detected.
The mechanical equipment has a limited service life and requires frequent checking and adjustment during production. Similar adjustment is naturally also required following the replacement of worn components in the checking equipment. On each such occasion the production tool must be stopped, replacement and/or adjustment effected and production restarted. Not until full production speed has all but been attained is it possible to see whether the measures taken have resulted in correct adjustment and proper operation of the checking equipment.
When the production tool retards or accelerates from or to full production speed, metal can tops are produced which must be scrapped. This is because the rivet is not correctly secured at low machine speeds.
Checking equipment so far used consequently entails numerous stoppages in production and each stoppage naturally reduces production volume. In addition to this, a number of defective metal can tops, which must be scrapped, are produced in connection with each stoppage.
Another disadvantage of the checking equipment presently used is that a loose pull-up ring or a piece of metal that has dropped into the seat of the production tool is often detected as a pull-up ring secured to the metal can top. A loose part of this kind in reality often causes damage to the metal can top or poor riveting of the pull-up ring. A large quantity of defective metal can tops may be produced if the situation is not observed through manual supervision.